/******************************************************************************

                              Online C++ Compiler.
               Code, Compile, Run and Debug C++ program online.
Write your code in this editor and press "Run" button to compile and execute it.

*******************************************************************************/
#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("oo.in");
ofstream fout("oo.out");
int n,v[100005],dp[100005],sol;
int main()
{
    fin>>n;
    for(int i=1;i<=n;i++)
    {
        fin>>v[i];
    }
    dp[0]=0;
    dp[1]=0;
    dp[2]=v[1]+v[2];
    for(int i=3;i<=n;i++)
    {
        dp[i]=max(dp[i-1],v[i-1]+dp[i-3]+v[i]);
    }
    sol=dp[n-1];
    dp[0]=0;
    dp[1]=0;
    dp[2]=0;
    dp[3]=v[2]+v[3];
    for(int i=4;i<=n;i++)
    {
        dp[i]=max(dp[i-1],v[i-1]+v[i]+dp[i-3]);
    }
    sol=max(sol,dp[n]);
    dp[0]=0;
    dp[1]=v[1]+v[n];
    dp[2]=0;
    for(int i=3;i<=n;i++)
    {
        dp[i]=max(dp[i-1],v[i-1]+v[i]+dp[i-3]);
    }
    sol=max(sol,dp[n-2]);
    fout<<sol;
    fin.close();
    fout.close();
    return 0;
}